Hilde, I hope it works out for you! Five bottles is a lot--I'm sure that will be a lot of work keeping up with them. But I agree that changing the bottle every three days would be way too much too!
I am hoping to switch my two bottles over to my 29 and see how that goes. With the 29 being a taller tank, the plants are more visible and have more room to grow upward. The problem is that on that tank I have a sponge filter. I could switch my power filter over to that tank, since it "chops up the bubbles," but then the back of the tank will be open and there's a chance my little kids could get into it. We'll see how it goes!